The primary component of plant cell walls, cellulose, is not only the most abundant biopolymer, but it is also a completely renewable resource. In order to expose cellulose, the lignocellulosic material made up of cellulose, hemicellulose and lignin, often requires a harsh chemical or temperature-based pretreatment to remove the hemicellulose and lignin. The cellulose is subsequently digested with mixtures of expensive cellulose-digesting enzymes, called cellulases. Digestion (by hydrolysis) of the cellulose by cellulases produces glucose which can be fermented into liquid fuel.
At this time, for the digestion of cellulose to be economically feasible, the cellulase production costs must decrease. For complete cellulose digestion, a mixture of wild type fungal cellulases is known to require at least three different activities: endoglucanase, cellobiohydrolase I, and cellobiohydrolase II, where each type of activity may be carried out by more than one enzyme. The filamentous fungus, Hypocrea jecorina (Trichoderma reesei) digests cellulose using the least number of cellulase enzymes, and the majority of the digestion is attributed to four enzymes: Cel7A, Cel6A, Cel5A, and Cel7B. As such, an enzymatic mixture made using these H. jecorina cellulases requires fewer components for complete digestion.